1. Field of the Invention
The invention relates generally to an agitator assembly for a washing machine and more particularly to an agitator assembly comprising an auger with a spiral vane.
2. Description of the Related Art
Automatic washing machines are widely known and commonly used to wash a load of clothes comprising one or more clothing articles in accordance with a programmed wash cycle. Clothes washers of this type typically comprise a perforated basket located within an imperforate tub, with the basket being rotatable relative to the tub. The clothing is placed in the basket where the wash liquid is free to flow between the basket and the tub through the perforations. Vertical axis immersion-type washing machines typically comprise a single- or dual-action agitator assembly within the basket, and the agitator assembly rotates relative to the basket about a vertical axis to impart mechanical energy to the submerged clothing. Single-action agitator assemblies comprise a reciprocating agitator having an agitator barrel and a skirt portion with circumferentially spaced vanes. The agitator vanes extend radially outward from the agitator barrel, and the lower edge thereof can be completely integral with the skirt or spaced from the skirt. The agitator vanes, along with the agitator barrel and the skirt, are typically injection molded polypropylene. Consequently, the vanes are relatively stiff and are substantially inflexible when they are integral with the skirt or flex only about an axis parallel with the vertical axis when the lower edge is spaced from the skirt.
Dual-action agitators incorporate an auger for driving the clothes down to the agitator. A traditional auger surrounds the agitator barrel and is coupled to the agitator by a unidirectional clutch. The auger typically comprises a tubular body and a continuous helical vane having a constant cross section. The helical vane is integral with and extends outwardly from the body and comprises a root portion where it meets the body and tapers outward to a tip. The helical vane can be perpendicular to the central axis of the body or, more preferably for better wash performance, undercut or inclined relative to the central axis, as shown in the above mentioned Pinkowski patent. Augers are preferably produced with an injection molding process. To accommodate the undercut of the helical vane, the injection molding process uses multiple radially-moveable mold sections surrounding a core, wherein after the material is injected into the core and sufficiently solidified, the molds are retracted radially while the core is simultaneously axially pulled from the molds.
The combination of the method of making the auger and the physical characteristics (continuous spiral, undercut vane, and constant radial cross section) creates a limit on the radial extent or width (the radial distance from the tubular body to the tip) of the helical vane and causes the helical vane to have a relatively thick root. The actual width of the vane is limited to a value less than the maximum vane width, which is the largest possible width for the vane. The thickness of the vane at the root and the maximum vane width depends on the degree of vane taper, which also referred to as the draft angle, from the root to the tip. The draft angle is a function of the undercut angle, which is the angle between the lower surface of the vane and the outer wall of the body, and the vane pitch, which is the distance between adjacent turns of the vane and is indicative of the slope of the vane. Assuming all other variables are constant, a larger undercut angle and a smaller pitch each individually corresponds to a smaller draft angle and, thus, a thinner root and a larger maximum vane width. However, the combination of a desired undercut angle and pitch to achieve a desired auger performance in prior art auger designs results in a relatively large draft angle and, thus, a thick root and a shorter width. As an example, some prior art auger vanes have a root that are on the order of 12-16 mm and a maximum vane width of about 33-35 mm. Corresponding ratios of vane width to root thickness for these values range from about 2.2-2.8, which means that the vane width is less than about 3 times the root thickness.
Unfortunately, a thick root can lead to several problems associated with the injection molding process and with the auger itself. For example, not only do such vanes require a large volume of material, but also the root must sufficiently solidify before the auger can be removed from the molds. As a result, the cycle times can be undesirably long, and the life of the mold is relatively short. Additionally, when the root is thick, the cylindrical body warps into an oblong, egg-like shape, and a depression or sink forms on the inside wall of the body at the vane because the root of the vane tends to pull the body outward while cooling. Because the auger fits over and rotates relative to the agitator barrel, the auger must be adapted to accommodate for warpage and sinks so that it is concentric with the agitator barrel.
To avoid the problems associated with thick roots, the undercut angle can be increased, and the pitch can be decreased to thereby decrease the root thickness. Such a solution would also increase the maximum vane width, which can increase the effectiveness of the auger. However, the undercut angle and the pitch are selected based at least partly upon the washing performance and efficiency of the washing machine, and it is undesirable to change the undercut angle and the pitch to the extent needed to achieve a large maximum vane width and a relatively thin root.
During use of the washing machine, the auger vane imparts a downward motion to the clothing articles and the wash liquid, and the agitator vanes impart a centrifugal motion to the clothing articles and the wash liquid. Hence, as the auger rotates in one direction and the agitator rotates reciprocally, the auger pushes the clothing articles from the surface of the wash liquid down towards the agitator, and the agitator pushes the clothing articles outward toward the basket. As the clothing articles approach the inner wall of the basket, the basket functions as a barrier to further centrifugal outward movement, and centrifugal pressure from the moving wash liquid and from other clothing articles is converted to higher static pressure. Increased static pressure pushes the wash liquid and clothing articles and some wash liquid and clothing articles move downward while the majority moves upward along the basket towards the surface of the wash liquid where they are pushed downward again by the auger. As a result, the clothing articles are washed as they move along a toroidal path, and one full cycle along this path is commonly referred to as a rollover.
Because the agitator relies on the interactions between the wash liquid, the clothing articles, and the basket to move the clothing articles upward, the agitator has to impart a large amount of mechanical energy to the clothing articles to maintain the movement thereof along the toroidal path and to achieve a desired number of rollovers. Friction losses during flow transmission from the outward movement to the upward movement require additional energy to transform flow from outward direction to upward direction. A motor drives reciprocal rotation of the agitator, and the rotational energy of the agitator is converted to the mechanical energy applied to the clothing articles. Larger mechanical energy requirements, therefore, can strain the motor and result in high electrical energy consumption. Additionally, clothing articles can collect at the bottom of the basket and impede movement of the clothes load along the toroidal path, which can lead to reduced washing performance and effectiveness of the washing machine.